Abstract: The present invention discloses a focus detection device capable of reading a plurality of focus detection outputs in parallel. As an exemplary structure, the focus detection device includes a focus detection sensor having a plurality of output terminals for outputting, in parallel, analog data corresponding to focus states of multiple points in the field of a viewfinder, a multiplexer for arranging and outputting, in series order on the one terminal, the analog data output in parallel from the plurality of output terminals of the focus detection sensor, and an A/D converter for converting, to digital data, the analog data arranged in series order on the one terminal through and output from the multiplexer.

Abstract: Disclosed are detecting apparatus for detecting statuses of an optical disc and methods thereof, which can avoid or reduce erroneous status decisions at the edge of a blank region. The detecting apparatus includes a blank detector, for detecting a blank region of the optical disc to generate a blank detection signal; an edge detector, for detecting a transition of the blank detection signal to generate an edge detection signal; a control circuit, in response to the edge detection signal for outputting control signals; and a defect detector in response to the control signals for detecting defect region of the optical disc to generate a defect decision signal.

Abstract: A disc with a temporary defect management information area and a defect management area includes a defect management area that is present in at least one of a lead-in area, a lead-out area, and an outer area, a temporary defect information area which is formed in the data area and in which temporary defect information is recorded, and a temporary defect management information area which is present in at least one of the lead-in area, and the lead-out area. Accordingly, it is possible to record user data in a recordable disc, especially, a write-once disc, while performing defect management thereon, thereby enabling efficient use of a defect management area having a limited recording capacity.

Abstract: Optical disk players include a disk spinning system that is configured to spin an optical disk at a constant linear velocity and a burst cutting area decoding system that is configured to decode data in a burst cutting area of the optical disk, while the optical disk is spinning at the constant linear velocity. The burst cutting area data decoding system may be configured to determine a rotational frequency of the optical disk while reading the data in the burst cutting area, and using the rotational frequency that was determined to decode the data in the burst cutting area that was read.

Abstract: An optical disc reading apparatus, such as a Near Filed optical disc reading apparatus, comprises a disc reader (401) which generates a first signal by reading an optical disc (403). A bit detector (407) detects data values in response to the first signal and data reference signals which are indicative of expected signals for different data sequences. An air gap processor (415) generates a reading head position error signal indicative of a distance between the surface of the optical disc and a reading leans. A reference processor (409) modifies the data reference signals in response to the reading head position error signal. The invention allows improved bit detection and in particular allows fast adaptation of e.g. a Partial Response Maximum Likelihood (PRML) bit detector to variations in an air gap for a reading lens.

Abstract: An information recording apparatus includes: a recording device capable of recording information into a data area of an information recording medium, by irradiating laser light, in conformity with a predetermined error correction method; an optimum-recording-power detecting device for obtaining an optimum recording power of the laser light, by recording test writing data into a data area portion with a length which is equal to or less than an allowable defect length in the predetermined error correction method, within the data area, by using the recording device; and a controlling device for controlling the recording device to record the information into the data area with the obtained optimum recording power.

Abstract: A method of managing a defective area in an information recording medium having a user data area, a replacement area, and a defect management information area is disclosed. The method manages the defective area using a block of a predetermined size as a unit of management. The method includes the step of, at the time of replacing a defective block including the defective area with a replacement block of the replacement area, dividing the replacement block into multiple sub-blocks, and setting identification information for identifying a first one of the sub-blocks to which data is relocated from the defective block and a second one of the sub-blocks to which no data is relocated from the defective block. The identification information is set in defect management information.

Abstract: This invention relates to a method of determining the location of a plurality of laser spots, comprising: determining a first distance of a first laser spot; determining a second distance of the first laser spot; determining a first distance of a second laser spot; determining a second distance of the second laser spot; and adjusting, if necessary, the locations of the first and second laser.

Abstract: An apparatus for and a method of compensating for a defect of an optical disc. The method includes: detecting a disc defect zone according to an RF sum signal level read from the optical disc; inverting a phase of a tracking error signal generated during a first specified time from the start of the defect zone; and holding a tracking servo control by adding components of the inverted tracking error signal to a tracking drive signal for a second specified time.

Abstract: The write-once recording medium has a data structure for managing temporary defect management areas, TDMAs, of the recording medium, where each TDMA is for at least storing temporary defect management information. In one embodiment, the recording medium includes a TDMA access indicator, TAI, area for selectively storing data indicating which one of the TDMAs is currently in use.

Abstract: A disc with a temporary defect management information area and a defect management area includes a defect management area that is present in at least one of a lead-in area, a lead-out area, and an outer area, a temporary defect information area which is formed in the data area and in which temporary defect information is recorded, and a temporary defect management information area which is present in at least one of the lead-in area, and the lead-out area. Accordingly, it is possible to record user data in a recordable disc, especially, a write-once disc, while performing defect management thereon, thereby enabling efficient use of a defect management area having a limited recording capacity.

Abstract: A recording medium for storing defect management information to record real time data, a defect managing method therefor, and a method of recording real time data. The recording medium stores information representing use or non-use of linear replacement defect management in which a defective area on the recording medium is replaced with the spare area, in order to record real time data. While maintaining compatibility between the defect managing method and a defect managing method based on a current DVD-RAM standard, i.e., while allowing a report of the fact that there are blocks which have not been linearly replaced, linear replacement is not performed when real time data is recorded. Thus, real time data can be recorded and reproduced.

Abstract: A recording medium for storing defect management information to record real time data, a defect managing method therefor, and a method of recording real time data. The recording medium stores information representing use or non-use of linear replacement defect management in which a defective area on the recording medium is replaced with the spare area, in order to record real time data. While maintaining compatibility between the defect managing method and a defect managing method based on a current DVD-RAM standard, i.e., while allowing a report of the fact that there are blocks which have not been linearly replaced, linear replacement is not performed when real time data is recorded. Thus, real time data can be recorded and reproduced.

Abstract: An optical disc playback apparatus includes an optical pickup, an RF amplifier that generates a tracking error (TE) signal based on an electrical signal from the optical pickup, a defect detector that detects a defect on the optical disc and that outputs a DFCT signal indicating the detected defect, a switch that outputs a hold signal when a defect is detected based on the DFCT signal, a driver that controls the optical pickup based on the output signal of the switch, a corrector that extracts an oscillation component of the optical pickup from the TE signal in response to the DFCT signal when a defect is detected and that outputs a correction signal indicating the oscillation component, and an adder that adds the correction signal from the corrector to the hold signal.

Abstract: A method of overwriting data in a write-once information storage medium and a data recording and/or reproducing apparatus therefor. In the data overwriting method, a command to overwrite new data in a first area of the write-once information storage medium where data has already been recorded is issued. Then, the first area is considered as a defective area, and the new data is recorded in a second area. Thereafter, updated defect management information, including information about the locations of the first and second areas, is recorded in the write-once information storage medium. Accordingly, overwriting can be performed in write-once information storage media, which is incapable of physical overwriting, by using a logical overwriting technique. Thus, data recorded in the write-once information storage medium may be changed or updated.

Abstract: An evaluation apparatus for obtaining an evaluation value of a signal read from an optical recording medium includes a reading device reading a signal recorded on the optical recording medium, an edge position detection device detecting edge positions of the read signal acquired by the reading device, a frequency distribution table generation device generating a frequency distribution table of the edge positions on the basis of accumulation result of information of the edge positions detected by the edge position detection device, and a first calculation device calculating a T degree value represented as [{?fi×(xi?A)(2m+1)}/F]{1/(2m+1)}??Formula 1 (wherein m is a natural number excluding zero) wherein, in the frequency distribution table generated by the frequency distribution table generation device, xi, fi, F, and A represent the value of each of the classes, the frequency of each of the classes, the sum of the frequencies, and the weighted average value, respectively.

Abstract: A method for managing a defective area of a write-once optical recording medium, and an optical recording medium using the same, are provided. The method includes steps of firstly writing replacement data in a predetermined area, the replacement data corresponding to a defective area detected during a data reproduction operation; secondly writing locator information in the predetermined area, the locator information indicating respective positions of the defective area and the corresponding replacement data; and thirdly writing a supplementary access pointer in a lead-in area, the access pointer for accessing the locator information written in the predetermined area. The predetermined area, which may be located inside or outside the data area, stores supplementary defect list information enabling data read operations when defective areas are newly detected by a host after recording data on a write-once type disc such as a BD-WO disc.

Abstract: An optical disc device includes an optical head section and a regularity monitoring circuit. The optical head section generates a wobble signal indicating wobbling of a track formed on a recording surface of an optical disc medium based on a reflected light reflected by the optical disc medium. The regularity monitoring circuit judges an existence or absence of a defect on the optical disc medium based on a difference between the wobble signal and a signal indicating the wobble under a normal condition.

Abstract: A recording medium for storing defect management information to record real time data, a defect managing method therefor, and a method of recording real time data. The recording medium stores information representing use or non-use of linear replacement defect management in which a defective area on the recording medium is replaced with the spare area, in order to record real time data. While maintaining compatibility between the defect managing method and a defect managing method based on a current DVD-RAM standard, i.e., while allowing a report of the fact that there are blocks which have not been linearly replaced, linear replacement is not performed when real time data is recorded. Thus, real time data can be recorded and reproduced.

Abstract: A write-once recording medium structure and an apparatus and method for recording final management information on the recording medium, are provided. The recording medium includes a temporary defect management area (TDMA) and a defect management area (DMA). The method includes transferring information recorded in the TDMA to the DMA of the recording medium and recording the transferred information in the DMA as final management information. The final management information includes at least one defect list and either space bit map information or sequential recording range information. The position information on one or all valid defect lists is recorded in the DMA.

Abstract: A write once disc includes a defect management area that is present in at least one of a lead-in area and a lead-out area; a temporary defect management area that is present in at least one of the lead-in area and the lead-out area; and a drive & disc information area that is present in at least one of the lead-in area and the lead-out area. Information regarding the locations of temporary defect information and temporary defect management information is recorded in the drive & disc information area, the temporary defect information and temporary defect management information, which includes drive & disc information, are recorded in the temporary defect management area, and temporary defect information and temporary defect management information, which are lastly recorded in the temporary defect management area, are recorded in the defect management area for disc finalization.

Abstract: An equalizer coefficients generator receives a DSS sequence and a DSS readback sequence, which is a function of a channel processing of the DSS sequence by a read channel. The generator generates a coefficient cyclic equalizer vector as a function of the DSS sequence and the DSS readback sequence. The generator further generates an error signal as a function of a comparison of the DSS sequence and an equalization of the DSS readback sequence based on the coefficient cyclic equalizer vector. An unacceptable error signal indicates a need to adjust the coefficient cyclic equalizer vector to yield an acceptable comparison of the DSS sequence and an equalization of the DSS readback sequence based on the coefficient cyclic equalizer vector.

Abstract: A defect detector in a data disc system includes a defect estimation unit and a defect length counter. The defect detector inputs a RF signal from a pick-up unit for generating a defect signal. The defect length counter interprets the defect signal using a wobble signal and a header position (ESFS) signal to generate defect length information. A system controller determines which sector of the data disc has unacceptable defect from the defect length information to reassign such a sector to another available sector on the data disc.

Abstract: A disc with a temporary defect management information area and a defect management area includes a defect management area that is present in at least one of a lead-in area, a lead-out area, and an outer area, a temporary defect information area which is formed in the data area and in which temporary defect information is recorded, and a temporary defect management information area which is present in at least one of the lead-in area, and the lead-out area. Accordingly, it is possible to record user data in a recordable disc, especially, a write-once disc, while performing defect management thereon, thereby enabling efficient use of a defect management area having a limited recording capacity.

Abstract: The requested data is read from a DVD disk by interruption in ST46. Then, the ID information for indicating the leading end of the data, and the result of the identification by use of the EDC for indicating whether or not the data is correct are stored in ST47. When the disk is identified as a DVD-video disk and the flag is set in ST 48, and also when the number of times N of retries is identified as being larger than NR in ST50 and the read data is not identified as control data in ST51, data transmission is performed. When no flag is set, the disk identification is performed based on whether or not the data at a predetermined position on the logical format has predetermined data in ST49. When it is identified that an error has been detected in ST52 and also when the number of times N of retries becomes larger than NS in ST53, the occurrence of an error is announced.

Abstract: A write once disc includes a defect management area that is present in at least one of a lead-in area and a lead-out area; a temporary defect management area that is present in at least one of the lead-in area and the lead-out area; and a drive & disc information area that is present in at least one of the lead-in area and the lead-out area. Information regarding the locations of temporary defect information and temporary defect management information is recorded in the drive & disc information area, the temporary defect information and temporary defect management information, which includes drive & disc information, are recorded in the temporary defect management area, and temporary defect information and temporary defect management information, which are lastly recorded in the temporary defect management area, are recorded in the defect management area for disc finalization.

Abstract: A data recording/reproducing method with robust error handling capability and a data recording/reproducing apparatus therefore, are provided. The data recording method includes: dividing data to be recorded on a recording medium into blocks having a predetermined size; repeatedly recording each block at a predetermined number of times on the recording medium, and recording the predetermined block size and the predetermined number of block recordings on the recording medium. According to the data recording method, it is possible to recover damaged data using a predetermined different block instead of a defective block by dividing data into blocks having a predetermined size and repeatedly recording the blocks on a recording medium a predetermined number of times, so that the recorded data has a robust defect resistance.

Abstract: A disc with a temporary defect management information area and a defect management area includes a defect management area that is present in at least one of a lead-in area, a lead-out area, and an outer area, a temporary defect information area which is formed in the data area and in which temporary defect information is recorded, and a temporary defect management information area which is present in at least one of the lead-in area, and the lead-out area. Accordingly, it is possible to record user data in a recordable disc, especially, a write-once disc, while performing defect management thereon, thereby enabling efficient use of a defect management area having a limited recording capacity.

Abstract: A disc with a temporary defect management information area and a defect management area includes a defect management area that is present in at least one of a lead-in area, a lead-out area, and an outer area, a temporary defect information area which is formed in the data area and in which temporary defect information is recorded, and a temporary defect management information area which is present in at least one of the lead-in area, and the lead-out area. Accordingly, it is possible to record user data in a recordable disc, especially, a write-once disc, while performing defect management thereon, thereby enabling efficient use of a defect management area having a limited recording capacity.

Abstract: The present invention is directed to a data recording method of notifying degree of deterioration of recording medium thus to perform stable recording operation. Even in the case where uncorrectable address read error does not exist, deterioration information is displayed in accordance with generated and stored deterioration information. Whether or not address read error of ATIP is detected over successive two frames or more, or whether or not four errors or more are detected on the average at 75 frames is discriminated. In the case where error detecting state is adapted to affirmative discrimination condition, warning is displayed. In the case where 200 errors or more detected from deterioration information generated in processing with respect to random missing with respect to written data exist on the average with respect to successive 750 frames, or in the case where one error or more detected in processing with respect to random missing exist, disc deterioration warning display is similarly performed.

Abstract: An information storage medium includes an area in which updated disc-related information and recording-related information updated with a change in at least one of a disc version number and a recording speed is recorded along with existing disc-related information and recording-related information. The existing disc-related information and recording-related information are recorded, and the updated disc-related information and recording-related information is recorded in an area in which the existing disc-related information and recording-related information is recorded. Accordingly, data can be recorded/reproduced on/from a new version of information storage medium even using an existing drive.

Abstract: When the data is reproduced by irradiating a laser beam onto the optical disk, an amount-of-irradiation-beam detection signal is produced according to the amount of the laser beam irradiated onto the optical disk, and the defect on the optical disk is detected on the basis of this amount-of-irradiation-beam detection signal. In addition, when the data is reproduced by irradiating the laser beam onto the optical disk, the amount-of-irradiation-beam detection signal is produced according to the amount of the laser beam irradiated onto the optical disk, an amount-of-reflected-beam detection signal is produced in accordance with the amount of the laser beam reflected from the optical disk, and the defect on the optical disk is detected on the basis of the amount-of-irradiation-beam detection signal and the amount-of-reflected-beam detection signal. Even when the optical disk has a defect, the laser beam is continuously irradiated onto the optical disk.

Abstract: A method for verifying whether a recording/reproducing apparatus properly produces disc management information and records the disc management information on a disc includes preparing a test disc; issuing reading commands to a recording/reproducing apparatus to be tested on which the test disc is loaded and verifying the disc in order to verify the reading operation; and issuing recording commands to the recording/reproducing apparatus to be tested on which the test disc is loaded and checking whether a temporary disc management area (TDMA) structure is properly updated on the disc in order to verify the modification operation.

Abstract: A method of verifying whether a recording and/or reproducing apparatus that records and/or reproduces a disc having temporary defect management area (TDMA) information properly produces the TDMA information, the method including producing TDMA information produced by performing a recording test according to a series of recording operations based on a scenario using a blank test disc as test information; and providing a result of the recording test by confirming the test information using reference test information for the recording test.

Abstract: A recording method and a recording apparatus capable of optimally arranging data on a write-once type optical disc. In a write-once type optical disc recording method with respect to a disc having a read-in, a user area, and a read-out by employing defect management information, the user area is divided into 3, or more pieces of R-zones; at least 2 recordable R-zones having recordable areas are present. When an unrecordable R-zone having no recordable area is present on the read-in side rather than two, or more pieces of the R-zones among the R-zones having the recordable areas, a linear replacement destination of a logical overwriting is determined to such an R-zone other than an R-zone having a recordable area, which is located adjacent to the unrecordable R-zone.

Abstract: When data is to be written on an optical disc in the unit of a sector, an attempt is made to read a block A to which a write sector belongs for the purpose of judging whether the block can be normally read. If the block A is not successfully read, it is judged to be a defective area, and an alternative write is performed in an alternative area in the unit of a sector. The alternative write may be performed so that a plurality of sectors belonging to the same block are dispersively written in different blocks d, E. When new data is to be written in a new sector in such a situation, data is acquired from the dispersed other sectors, merged with the new data, and collectively rewritten in the same block E.

Abstract: A maximum likelihood decoder includes metric generators for generating metrics based on a plurality of partial responses and a Viterbi decoder for realizing maximum likelihood decoding by using a synthetic metric generated by synthesizing the metrics. A first partial response is an original partial response. A second partial response is a differential response generated by subtraction by shifting the first partial response by 1 clock. Alternatively, the differential response may be generated by subtraction by shifting the first partial response by 2 clocks. The second partial response may be a response generated by addition by shifting the first partial response by 2 clocks. Alternatively, the second partial response may be an integration response generated by adding all previous samples of the first partial response.

Abstract: At least one detection area on an optical storage medium is allocated for data storage first, and then the detection area is set to a defect detection mode of either write detection or write verification, depending on the number of defects stated in a previous defect record. If the detection area is the write detection mode and the number of accumulated defects exceeds a default threshold value, the detection area would be configured anew and thereby set to a defect detection mode of write verification.

Abstract: A method and device for protecting an optical disc from being damaged when a defect is encountered during recording. According to the present invention, when a defect is encountered during recording, the length of the defect is measured. The recording is stopped when the length of the defect exceeds a threshold. After the defect has been passed, the recording can be resumed.

Abstract: In order to enhance the usability of a write-once recording medium, the recording medium is provided with an ordinary recording/reproduction area, an alternate area, a first alternate-address management information area and a second alternate-address management information area. In addition, written/unwritten state indication information is recorded in a predetermined area. The second alternate-address management information area is an area allowing alternate-address management information recorded therein to be renewed by adding alternate-address management information to the area. Alternate-address management information recorded in the second alternate-address management information area includes information recorded in a first information format and information recorded in a second information format. The first information format shows an alternate source address and an alternate destination address for each data unit.

Abstract: The present invention provides a method or an apparatus for recording data additionally by acquiring replacement data easily even when the latest disc management information cannot be read out of the disc. When updating TDMS (Temporary Disc Management Structure), an update reason of a corresponding TDMS and a TDDS (Temporary Disc Definition Structure) start address in a previously recorded TDMS are recorded in disc management information as additional information. If the latest TDMS cannot be read out of the disc but the additional information can be read out, the additional information are referred to determine the latest LRA for use in additional data recording on the disc.

Abstract: When user data fails to be recorded in an address of a user data area, the same data is recorded in an address of a spare area. Information indicating that the data for the address of the user data area is recorded in the address of the spare area is registered in a DL that is loaded in a buffer memory, and the information is recorded in a currently-valid DL area of DMA1. As similar thereto, the information is recorded in a currently-valid DL area of DMA2. If the recording fails, the DL is alternatively recorded in another DL area of the same DMA2. Thereafter, DDSs of DMA2 are deleted, and then, without changing information of the number of times of updating the DDSs, only the staring address of the DL of the DDSs is updated. According to the updating method, it is possible to shorten the time required for updating management information of a medium in an information recording/reproducing apparatus.

Abstract: A method and device for searching a recording medium are provided. The recording medium has a management information area of which location information is overlapped with that of a program area. The method for determining an area on a recording medium having an overlapped time range between two areas reads a time address from a current position on the recording medium, obtains additional information from the recording medium or from a recording medium driving unit, if the read time address belongs to the overlapped range, and determines, based on the obtained additional information, to which one the areas the current position belongs. Therefore, it prevents wrong track jumps that are caused from time-overlapped areas on a capacity-expanded recording medium.

Abstract: An apparatus for scanning a track on a record carrier has a head (22) and front end circuitry (31) for scanning the track and generating scanning signals. A detection unit (32) detects anomalies in the scanning signal, for example for adjusting a tracking servo. The detection unit (32) calculates a mean value of the scanning signal and compares the mean value to a threshold for providing an anomaly detection signal (33). Further a classification unit (34) provides an indication of the type of defect for determining a suitable responsive or corrective action.

Abstract: A method for real time recording and playback of data to and from an optical recording medium, and a method for managing a file thereof is disclosed. In the present invention, the host controls real time data writing by providing a signal requesting for information on a defective area to the device for recording/playback of data to/from an optical disk before providing a write command. Accordingly, the write command is generated such that data is not written on the defective areas, based upon the returned information on the defective area. Alternatively, the host may first provide a write command to the device for recording/playback of data to/from an optical disk, upon which information on defective areas is returned. Thus, the host generates and provides a new write command such that data is not written on a defective area based upon the returned information on the defective area.

Abstract: When user data is recorded on a write-once medium, linking variations can be reduced that are produced as management information for managing the user data is updated by additionally recording on and off, thereby assuring the reliability of the reproduction compatibility of the DVD player. Before the final file of the management information is recorded, dummy data of a plurality of successive blocks are recorded at a time by a single operation, and then the final file is additionally recorded after the dummy data. Therefore, the linking precision can be prevented from being degraded in the linking portions of the management information, and thus the management information can be properly read when the DVD player makes compatible reproduction of the medium.

Abstract: The present invention relates to a method of detecting a defect area without any mistake during data recording on a writable disk. This method detects a level of a servo error signal produced during a recording operation, checks whether the servo error signal is in an abnormal state based on the detected level, detects a periodic wobble signal or periodicity of the abnormal state occurrences of the servo error signal produced during the recording operation, and determines whether a recording area is in defect based on successful decoding of the detected periodic wobble signal or the periodicity of the abnormal state occurrences if the servo error signal is in an abnormal state. This method ensures exact detection of a defect area, whereby unnecessary speed reduction can be eliminated and successful data writing can be also guaranteed even in a defect area.

Abstract: A method by which, in an optical disk recording and reproducing device, the time required for a test recording performed prior to an actual information recording can be reduced according to characteristics of an optical disk. A random pattern signal is transmitted from a random pattern signal generating circuit 3 and recorded on a test track on an optical disk 1, and a bit error rate of a reproduction signal is measured. Only when a value of the bit error rate is not less than a fixed value, test pattern signals are transmitted from a test pattern signal generating circuit 4 and recorded. An edge timing of a reproduction signal is measured by an edge timing detecting circuit 13. Based on a result of the measurement, edge positions of a front-end pulse and a back-end pulse are corrected.

Abstract: A defect detector in an optical disk drive is presented. The defect detector indicates a defect by monitoring a sum signal. The sum signal is calculated from optical signals from detectors in an optical pick-up unit of the optical disk drive. A defect can be indicated when a filtered sum signal, the filtered sum signal being the sum signal filtered with a high pass filter, is above a threshold value. In some embodiments, the defect detector can recognize changes in laser power or transitions between media types and not indicate defects during those occurrences.

Abstract: A sampling clock generator for BCA data decoding providing a sampling clock, which is proportional to the actual rotation speed of a disk. The sampling clock generator includes a frequency counter, a divider and a frequency divider. The frequency counter counts the number of pulses of a reference clock for each period of a rotation speed indicating signal of a spindle motor and generates a counting value. The divider divides the counting value by a predefined value and generates a divided value. The frequency divider is employed to generate the sampling clock. The frequency divider receives the reference clock and divides the frequency of the reference clock by the divided value to generate the sampling clock. The frequency divider also adjusts the phase of the sampling clock according to the BCA reproducing signal.